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This post helps illustrate how researchers can start with a simple experiment and then move to a factorial design (both designs here are IVxPV designs).
In this story covered by KHOU, (originally in the Washington Post) we learn that when people hold hands during a stressful situation, it can help lower blood pressure and perceived stress.
In one study, researchers had couples hold hands during a scary movie. That small act helped limit the stress on our nervous system, calming parts of the brain responsible for vigilance and emotional response.
In the study above, the researchers (Graff et al., 2021) had a group of 83 couples watch 10-minute clips from horror movies. They randomly assigned half of the participants to watch alone, and the other half to hold hands with their spouse while watching. (In the hand-holding condition, they measured the pupils of one person while their comforting spouse wore headphones and was not able to see the movie.) The researchers used eye trackers to measure pupil dilation as a measure of stress during the movie. Pupillometry has shown that when people are under stress, their pupils dilate. Researchers use cameras to measure this pupillary response.
The researchers found that the pupils of the participants who watched the scary movie alone dilated more (indicating more stress) than those of people who watched while holding hands with their partner.
So far, this is a simple experiment.
a) Classify its key variables (so far) using the chart below.
| Variable name | What are the variable's possible levels? | Is this manipulated or measured? | Is this an IV, PV, or a DV? | For the IV/PV: Is it within-groups or between-groups? |
Now to introduce a second element of the study. These researchers gave each couple a questionnaire called the Social Relationship Index (SRI) to measure the quality of their relationship. Some of the couples were classified as "supportive" and others as "ambivalent."
b) Return to the table of variables and add this new variable to the chart above. Hint: Rather than being a true IV, this is a PV, or Participant variable.
c) The addition of this relationship quality variable makes this study into a factorial design. It's a 2x2. Is this a 2x2 independent-groups factorial? A 2x2 within-groups factorial? Or a 2x2 mixed factorial? Explain your answer.
d) The results found that in the groups holding hands (compared to watching alone) there was lower pupil dilation for all couples, but the effect was especially strong among supportive couples. Sketch this result. Put the DV on the y-axis and put the two hand-holding conditions on the x-axis. Use different line or bar graph colors for supportive and ambivalent couple types.
e) Estimate the main effects and interactions following this sentence structure:
There [was/was not] a main effect for the hand-holding condition, such that pupil dilation was higher for the __________ condition than the _______ condition.
There [was/was not] a main effect for the couple support type, such that pupil dilation was higher for the __________ couples than the _______ couples.
There was an interaction, such that__________.
Now here's another study that measured the same question, with a slightly different design. The journalist described this study as follows:
It matters whose hand we are holding.
A very small study on married women found holding a stranger’s hand did lower stress levels. However, that effect was even more pronounced when they held their husband’s hand.
In this "very small study" the researchers (Coan et al., 2006) had 16 heterosexual married couples participate. The wives were the focus of the study. The wives lay in an fMRI scanner, and over several minutes, they were subjected to a series of minor electric shocks. As you might imagine, this is a stressful experience! During one block of shocks, the held their husbands' hands. During another block, they held the hand of a male stranger they could not see. And during another block, they did not hold anyone's hand. These three blocks were counterbalanced. The researchers measured activity in brain regions that respond to stress. As the journalist reports, holding a stranger’s hand did lower stress levels. However, that effect was even more pronounced when they held their husband’s hand.
f) Classify its key variables (so far) using the chart below.
| Variable name | What are the variable's possible levels? | Is this manipulated or measured? | Is this an IV, PV, or a DV? | For the IV/PV: Is it within-groups or between-groups? |
Now for the PV. The journalist wrote, about this study:
For couples with the highest scores on marital quality tests, that stress relief was even more significant. So basically, the better the relationship, the more hand-holding helped.
The Coan team also measured relationship quality, this time using the Dyadic Adjustment Scale. Assume there were two groups for relationship quality: high quality and low quality.
g) Return to the table of variables and add this new variable to the chart above. Hint: Once again, this new variable is a PV, or Participant variable.
h) Again, the addition of this relationship quality variable made this study into a factorial design. So the design is now a 3x2. Is this a 3x2 independent-groups factorial? A 3x2 within-groups factorial? Or a 3x2 mixed factorial? Explain your answer.
i) The results of the Coan study found that while holding hands with their husband (compared to holding hands with a stronger or with nobody) women had lower stress responses in the brain. And, the drop was especially strong among wives who reported the best relationships. Sketch this result. Put the brain activity DV on the y-axis, Put the three hand-holding conditions on the x-axis. Use two different line or bar graph colors for high and low relationship quality.
Link to the hand-holding study with scary movies and pupil dilation (Graff et al., 2021) in PLOSOne.
Link to the hand-holding study with shocks and brain scans (Coan et al., 2006) in Psychological Science.
